Browsing by Author "Huang, Jie"

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    A Preliminary Study of Threonine Deaminase Duplication in Solanaceae
    (2013) Huang, Jie

    One of the most important questions in evolutionary biology is how new genes and new functions arise and evolve. Among the theories addressing this question, gene duplication is one of the most popular. Previous study has shown that two threonine deaminase (TD) gene copies exist in Solanum lycopersicum, and these two copies have very different functions and low sequence similarities. The primary objective of this study was to widen our understanding of this gene duplication and the subsequent evolutionary processes affecting the duplicate copies by first collecting additional TD sequences from related species, building a gene tree, and inferring the point of gene duplication. The evolutionary processes acting on this gene were then analyzed using the program PAML. Results indicate that 1) The TD duplication probably occurred in before the split of the Solanoideae from the Nicotianoidea; and 2) there is strong evidence for positive selection on one of the TD copies after gene duplication, while for the other TD copy, only weak evidence for positive selection was found; and 3) adaptive improvement of the copy with new function probably spanned a period of at least 25 million years.

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    beta-arrestin-1 competitively inhibits insulin-induced ubiquitination and degradation of insulin receptor substrate 1.
    (Mol Cell Biol, 2004-10) Usui, Isao; Imamura, Takeshi; Huang, Jie; Satoh, Hiroaki; Shenoy, Sudha K; Lefkowitz, Robert J; Hupfeld, Christopher J; Olefsky, Jerrold M
    beta-arrestin-1 is an adaptor protein that mediates agonist-dependent internalization and desensitization of G-protein-coupled receptors (GPCRs) and also participates in the process of heterologous desensitization between receptor tyrosine kinases and GPCR signaling. In the present study, we determined whether beta-arrestin-1 is involved in insulin-induced insulin receptor substrate 1 (IRS-1) degradation. Overexpression of wild-type (WT) beta-arrestin-1 attenuated insulin-induced degradation of IRS-1, leading to increased insulin signaling downstream of IRS-1. When endogenous beta-arrestin-1 was knocked down by transfection of beta-arrestin-1 small interfering RNA, insulin-induced IRS-1 degradation was enhanced. Insulin stimulated the association of IRS-1 and Mdm2, an E3 ubiquitin ligase, and this association was inhibited to overexpression of WT beta-arrestin-1, which led by decreased ubiquitin content of IRS-1, suggesting that both beta-arrestin-1 and IRS-1 competitively bind to Mdm2. In summary, we have found the following: (i) beta-arrestin-1 can alter insulin signaling by inhibiting insulin-induced proteasomal degradation of IRS-1; (ii) beta-arrestin-1 decreases the rate of ubiquitination of IRS-1 by competitively binding to endogenous Mdm2, an E3 ligase that can ubiquitinate IRS-1; (iii) dephosphorylation of S412 on beta-arrestin and the amino terminus of beta-arrestin-1 are required for this effect of beta-arrestin on IRS-1 degradation; and (iv) inhibition of beta-arrestin-1 leads to enhanced IRS-1 degradation and accentuated cellular insulin resistance.